Conventionally, plastics have characteristics such as processibility and usability, whereas, they have been thrown away after use owing to their difficulty in recycling, and to hygienic point of view. However, as the use and disposal of the plastics increase, problems associated with their disposal by landfilling or incineration have drawn attention, and they may be responsible for great burden on the global environment such as deficiency of garbage landfill sites, influences on ecological system by remaining nondegradable plastics in the environment, generation of detrimental gas in combustion, global warming resulting from a large amount of combustion calorie, and the like. In recent years, biodegradable plastics have been extensively developed as a material which can solve the problems of the plastic waste.
Additionally, these biodegradable plastics are of plant origin, and absorb and immobilize carbon dioxide that is present in the air. Carbon dioxide generated in combustion of these biodegradable plastics of plant origin was originally present in the air, therefore increase in carbon dioxide in the ambient air is not caused. This phenomenon is referred to as “carbon neutrality”, which tends to have been placed importance thereon. Carbon dioxide immobilization is expected to be effective in preventing the global warming. Particularly, in connection with Kyoto Protocol in which achievement level of carbon dioxide reduction was suggested, deliberation of Congress for ratification was approved in Russia in August 2003. Accordingly, it is highly probable that the Protocol will come into effect actually, whereby materials for carbon dioxide immobilization have drawn a great deal of attention, and active use thereof has been desired.
Meanwhile, although aromatic polyesters have been produced and consumed in large quantities as general-purpose polymers, in light of immobilization of carbon dioxide and prevention of global warming, they are not preferable material in terms of the carbon neutrality, because they are produced from fossil fuels, thereby leading to release of carbon dioxide immobilized in the ground to the ambient air.
In light of the biodegradability and carbon neutrality, aliphatic polyester-based resins have drawn attention as the plastics of plant origin, particularly polylactic acid-based resins, poly 3-hydroxyalkanoate (hereinafter, may be referred to as “PHA”), further poly[3-hydroxybutyrate-co-3-hydroxyhexanoate] (hereinafter, may be referred to as “PHBH”), and the like have been drawing attention.
Among them, poly[3-hydroxybutyrate-co-3-hydroxyhexanoate], in particular, has superior heat resistance owing to the crystallinity, and impact resistance, superior tensile elongation characteristics and flexibility resulting from 3-hydroxyhexanoate included as a copolymerization component, in combination. Therefore, they have drawn attention as a resin material accompanied by the balance of physical properties.
However, with respect to PHA, further greater impact resistance, tensile elongation characteristics, and moldability have been demanded, and improvement for time dependent alteration at room temperatures has been also demanded.
In this respect, improvement by adding a certain plasticizer was proposed (Patent Documents 1 to 3). However, bleed out properties, and volatility are not sufficiently improved by them, and polylactic acid is predominantly used as a biodegradable polymer. Moreover, any effect of improving the time dependent alteration is not referred to at all.
Furthermore, in order to improve the molding processibility of PHA, addition of another PHA having a higher melting temperature as a nucleating agent to PHA as a matrix was proposed (Patent Document 4), but significant time dependent alteration of physical properties was caused, and also a low level of tensile elongation characteristics was observed.
Patent Document 1: Japanese Examined Patent Application, Publication No. H07-68443
Patent Document 2: Japanese Unexamined Patent Application, Published Japanese Translation of a PCT Application No. 2005-501927
Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2002-80703
Patent Document 4: Japanese Unexamined Patent Application, Published Japanese Translation of a PCT Application No. H08-510498